1. Field of the Invention
The present invention relates to a scintillator panel, a radiation detector and manufacture methods thereof, and more particularly to a radiation detector to be used with a medical X-ray diagnosis apparatus, a non-destructive inspection apparatus or the like and its manufacture method.
In this specification, the term “radiation” is intended to include electromagnetic waves such as X-rays, α-rays, β-rays and γ-rays.
2. Related Background Art
Digitalization is accelerating in the field of medical apparatuses. There is a paradigm shift of Roentgen photography from a conventional film screen type to an X-ray digital radiography type.
FIG. 15 is a cross sectional view of an X-ray detector. As shown in FIG. 15, a scintillator panel 110 has: a phosphor layer 113 made of column-shaped crystallized phosphor; a base member 111 for supporting the phosphor layer 113; a reflection layer 112 made of an aluminum thin film for reflecting light converted by the phosphor layer 113 toward a sensor panel 100 to be described later; and a protective layer 114 made of organic resin for protecting the phosphor layer 113 and the like from external air.
The sensor panel 100 has: a glass substrate 101; a photoelectric conversion unit 102 made of photosensors and TFT's of amorphous silicon; a wiring unit 103 for transferring electric signals converted by the photoelectric conversion unit 102; and a protective layer 104 made of silicon nitride or the like for protecting the photoelectric conversion unit 102 and wiring unit 103.
The sensor panel 100 and scintillator panel 110 are bonded together by an adhesion layer 120, and this assembly is sealed with a sealing member 140. In order to suppress a variation in resolutions, it is necessary to precisely control the thickness of each layer through which light transmits. It is particularly necessary not to make the adhesion layer 120 too thick. To this end, after the adhesion layer 120 is coated between the sensor panel 100 and scintillator panel 110, this assembly is pressed by a roller so as not to make the adhesion layer 120 too thick.
In FIG. 15, reference numeral 115 represents a projection of about several tens μm to several hundreds μm which is partially formed, while the phosphor layer 113 is crystallized in a column-shape, by abnormal growth to be caused by dusts, splashes during evaporation, irregular surfaces of the base member 111 or the like. FIG. 15 schematically shows the scintillator panel having such projections.
FIG. 16A is an enlarged view showing the bonded portion between a sensor panel 100 without a projection and a scintillator panel 110. FIG. 16B is an enlarged view showing the bonded portion between a sensor panel 100 with a projection 115 and a scintillator panel 110. In FIG. 16B, h0 represents a thickness of the adhesion layer 120 near the projection 115, and T0′ represents a thickness of the adhesion layer 120 at a position apart from the projection 115.
A downward incident X-ray transmits through the base member 111 and reflection layer 112 and is absorbed in the phosphor layer 113 which in turn radiates visible light. Since this visible light propagates in the phosphor layer 113 toward the sensor panel 100 side without diffusion, it transmits through the protective layer 114, adhesion layer 120 and protective layer 104, and becomes incident upon the photoelectric conversion unit 102.
The incident visible light is converted into an electric signal by the photoelectric conversion unit 102, and read to the external via the wiring unit 103 under the switching control. In this manner, the X-ray detector shown in FIG. 15 converts input X-ray information into a two-dimensional digital image.
If the scintillator panel having projections on the surface of the phosphor layer such as shown in FIG. 15 is bonded to the sensor panel, the projection may break a photosensor of the photoelectric conversion unit or the wiring unit as shown in FIG. 16B. If the tip of the projection is sharp, this sharp tip easily enters the photosensor or wiring unit and breaks it. If a photosensor is broken, a pixel defect is generated in a digital image, whereas if a wiring unit is broken, a line defect is generated. If the bonding process is performed, the center of the projection is depressed and the phosphor layer becomes thin in the depressed area. The radioactive amount in the depressed area may become different from other areas, which lowers photosensitivity.
Even if the height of a projection is low and the photoelectric conversion unit is not broken, the projection is pushed by the sensor panel so that the phosphor layer is warped about the projection and the thickness h0 of the adhesion layer becomes larger than the thickness T0′. The width of scattered visible light incident upon the photoelectric conversion unit may change, which lowers the resolution of a digital image. The adhesion layer may be made thick so that the projection does not break a photosensor or the like and is accommodated in the adhesion layer. In this case, however, as shown in FIG. 19, since a gap between a wavelength conversion layer and sensor panel becomes large, the resolution of a digital image lowers. A practical resolution response is generally 0.7 or larger. In order not to set the resolution response to a value smaller than 0.7, it is preferable to make the adhesion layer thin.
The presence of a projection may allow air bubbles to enter the adhesion layer and adhesive agent cannot be distributed uniformly.
It becomes difficult to perfectly cover the surface of the phosphor layer if there is a projection. If the phosphor layer is made of CsI or the like, the phosphor layer may be dissolved because of deliquescence of CsI.